2018 Impact factor 1.686
Soft Matter and Biological Physics


Eur. Phys. J. E 4, 201-208

Nanoparticle chain-like formation in electrical double-layered magnetic fluids evidenced by small-angle X-ray scattering

R. Itri1, J. Depeyrot2, F.A. Tourinho3 and M.H. Sousa3

1  Instituto de Física da Universidade de São Paulo, Caixa Postal 66318, São Paulo, SP, 05315-970, Brazil
2  Complex Fluids Group - Instituto de Física - Universidade de Brasília, CP 04455, 70919-970 Brasília (DF), Brazil
3  Complex Fluids Group - Instituto de Química - Universidade de Brasília, CP 04478, 70919-970 Brasília (DF), Brazil

itri@if.usp.br

(Received 28 February 2000 and Received in final form 28 August 2000)

Abstract
Small-angle X-ray scattering (SAXS) was performed on a series of Electric Double-Layered Magnetic Fluids (EDL-MF) composed of ferrite type- CoFe2O4, MnFe2O4, ZnFe2O4, NiFe2O4 and CuFe2O4-nanoparticles of different crystalline sizes ($D_\ab{XR}$ ranging from 40 to 139Å, as determined by X-ray diffraction). The information concerning the scattering objects was obtained through the analysis of the distance distribution function p(r) and of the size distribution function D(R), both retrieved from SAXS data. The results show that EDL-MF, in the absence of an applied magnetic field, are composed of small magnetic particle aggregates in solution. These agglomerates are elongated in one direction (chain-like) with the longest dimension varying from 240 to 330Å. The cross-section size is of the order of $D_\ab{XR}$. The data also demonstrate that the maximum dimension of these aggregates is independent of the ferrite type. On the other hand, the number of aggregated magnetic particles is nanoparticle-size-dependent. Accordingly, larger ferrite-type nanoparticles as those with $D_\ab{XR}=139$Å form aggregates composed of 2-3 magnetic particles, whereas smaller ones with $D_\ab{XR}
\cong40$Å form agglomerates of about 6 magnetic particles in solution. As the nanoparticle size is reduced, it might increase the particle surface defects. Such occurrence would affect the particle surface charge density, which could reduce the electrostatic screening, favoring the agglomeration phenomenon.

PACS
75.50.Mm - Magnetic liquids.
75.50.Tt - Fine-particle systems.
61.10.Eq - X-ray scattering (including small-angle scattering).


© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001